Over the years, various theories have been advanced to account for the clinical manifestations of autism. These theories have each proposed a localization for the neuropathology within the neuraxis as well as a theory about the nature of the pathophysiology. Overall, these theories have postulated pathology at three different levels within the neuraxis-- the cerebral cortex, the limbic system, and the posterior fossa. The purpose of this project is to examine evidence for the three competing brain localizations hypothesized in autism-- the cerebral cortex, the limbic system and the posterior fossa. A related purpose is to provide evidence, where possible, which will evaluate different theories at the same localization, e.g., the association cortex theory, the auditory processing theory and the selective attention theory of the cerebral cortex, and the brainstem theory and the cerebellar theory. These goals will be pursued with selected neuropsychologic, oculovestibular, and magnetic resonance imaging measurements. The results of this proposed study will be compared with the brain neurochemistry results from the investigators' study of in vivo 31p NMR spectroscopy study in autism. The subjects for this study will be 60 non-mentally retarded autistic individuals and 60 age, IQ, sex and race matched normal controls who will be recruited over four years. When added to the subjects from the initial two year study, this will result in a cohort of 90 autistic individuals and 90 matched controls by the end of this study, with 30 autistics and 30 controls in each of three age groups-- children, adolescents, and young adults. All subjects will be studied at entry and the children and adolescents from the initial two year study and the first year of this study will be reevaluated at the end of three years.